It is often necessary to ship precut sheet steel overseas to foreign purchasers and manufacturers. Such shipping requires that the steel be produced in a form amenable to packaging and further requires that the packaging provide protection against corrosion damage that may occur as a result of exposure to moisture.
Sheet steel emerges from the production mill in the form of a long single sheet which is coiled into a roll. When the steel is to be packaged for shipping, a roll is transported to the cutting area and loaded onto a spooling and cutting device. A portion of the roll is played out and a shear descends to cleave a rectangular sheet of steel from the roll. The playing out and shearing process is performed in a continuous motion such that many sheets of steel are cut from each roll. Running speeds of such a shear line often approximate 350 feet of steel per minute.
Typically, as each sheet is cut from the roll it is carried along a conveyor belt via motorized conveyor rollers to the packaging area. At the packaging area each sheet passes beneath an overhanging conveyor belt assembly capable of being magnetized so as to lift each sheet from the conveyor roller assembly and secure it to the overhanging belt. The overhanging belt then transports each sheet until it is positioned over a piling device, further described below. The overhanging belt is then demagnetized such that the sheet steel is released, and the forward and downward motion of the sheet carries it into the piling device below. In this way, a number of steel sheets are stacked on top of each other in the piling device.
The piling device provides a means for straightening the stack of steel sheets prior to packaging such that the edges of all the sheets are aligned with each other. The device comprises a rectangular base portion upon which the stack of sheets rests, the base having planar dimensions roughly similar to those of a steel sheet. Rollers may be incorporated into the base to facilitate removing a completed stack from the piling device. Five moveable straightening rams are arranged around the base and extend upward perpendicular to the plane base. Two of the moveable rams are spaced along each opposing long side of the base and a single ram is positioned at the center of one shorter side. At the other shorter side of the base is located a stationary vertical wall.
The straightening rams serve two purposes. First, they act as guides for the steel sheets as they drop from the overhanging conveyor assembly to the base. The sheet's forward motion as it drops from the moving overhead conveyor assembly causes one shorter end of the sheet to strike the end movable ram. The forward motion of the sheet is arrested and it drops to the stack, the moveable rams roughly aligning the sheets on top of each other.
Second, each moveable ram is pneumatically driven in a reciprocating motion perpendicular to its corresponding side of the base so as to contact the edges of the stack of steel sheets. Thus, the stack is straightened along the long edges by the synchronously opposing and compressing motion of the two sets of straightening rams located along the long side of the base. The stack is straightened along the short end by the motion of the single straightening ram located along the short end. This ram forces the stack to abut against the stationary wall, causing the short edges of the individual sheets to align with each other. Thus, the action of the moveable rams in conjunction with the stationary wall works to produce a stack of steel sheets sufficiently aligned for packaging.
In some prior art packaging assemblies the packaging process begins in the piling device. Prior to any introduction of steel sheets into the device a heavy paper lining, substantially larger than the steel sheets, and sometimes treated with corrosion resistant chemicals, is placed on the base of the piling device. Steel sheets are then stacked on top of the lining as above described. When the stack contains the proper amount of sheets the stack and lining combination is removed from the piling device. The lining is then folded up and around the sides and top of the stack and sealed. Thus, the lining completely encloses the stack of steel sheets. To provide stiffness to the stack, laborers then apply a piece of angle iron to each of the twelve edges of the lined stack and join together the fasten steel straps around the bundle and pieces of iron. The straps also secure the bundle to underlying 4.times.4 timbers which permit the bundle to be handled by a forklift. The assembly as described is then shipped, often overseas.
Significant drawbacks attend such a package assembly. The vast majority of the surface area of the stack is covered only by the thin paper lining, which is highly susceptible to puncture or tearing. A puncture hole can allow moisture to contact the stack, causing corrosive damage that the lining is meant to prohibit. The possibility of puncture is heightened by the lack of structural stiffening of the stack prior to and during the application of the angle iron. The lack of stiffening may allow the stack to become skewed during handling. Such skewing causes sharp edges and corners of sheets within the stack to protrude and contact the paper lining, causing punctures to occur.
Further, the application of the angle iron to the stack is a time consuming, labor intensive task, which uses relatively expensive material. Packaging costs under this method typically approximate 35 to 40 dollars per ton. Also, the resultant uneven package exterior detracts from the ability to stack the packages stably on top of each other, and further, renders the package more susceptible to damage by inadvertently catching the protruding angle iron on another package or other object.
Thus, it is desirable to provide a package assembly for stacked sheet steel which is more protective and more manageable, while also being lighter in weight, less expensive, less labor intensive, and less susceptible to damage than the existing assemblies.
The present invention fulfills these needs. The package fully encloses the steel sheet stack with rigid material, such as low grade steel, which is difficult to inadvertently penetrate. The invention provides stiffening of the stack from the beginning of the stacking process, and is extremely easy and inexpensive to assemble. The packaging cost using the invention is reduced to approximately 15 dollars per ton, as compared to the 35 to 40 dollars per ton cost of previous packages. The exterior surfaces of invention are uniform and very amenable to stable stacking of packages.